In modern communication technology it is becoming increasingly more important to be able to electronically detect the progress of a calling connection. One reason this is important is so that in automatic systems, particularly predictive dialing systems such as disclosed in concurrently filed copending patent application assigned to a common assignee, which patent is hereby incorporated by reference herein, the system is able to ascertain the status of any calling connection with a high degree of certainty.
It is not acceptable just to know that the call has not been answered, but the value of such a system lies in its ability to distinguish between no answer, busy, a dedicated computer or fax line, operator intercept, modems, etc. By knowing this information, the calling system can make determinations about future calls. For example, if a fax machine answers a call, there is no point in leaving a voice message or in retrying that call to that number. On the other hand, if a busy condition is detected, a call can be retried sooner than it would be if a no-answer condition were to be found.
Typically, the prior art in one form or another detects the envelope of the call progress signals. These envelopes are a result of the dual tones which are used for creating the various call progress audio signals. Such a system, however, does not work well in all countries, particularly where the telephone systems do not have standard tones which define the call progress signals.
In addition to the problem encountered where there are no signal envelopes, the prior art systems do not handle the situation where there is an answer by an attendant or by a fax machine or computer.
Another prior art method of determining call progress is to measure the on and off times of the audio signals, and from the change in cadence of these signals, deduce that a call has been answered. Again, this system cannot discriminate between answering machines, fax equipment, etc.
Accordingly, there exists in the art a need for systems and methods of determining the progress of calling connections without resort to signal timing or signal envelope detection.